From Ultraslow to Fast Lithium Diffusion in the 2D Ion ConductorLi0.7TiS2Probed Directly by Stimulated-Echo NMR and Nuclear Magnetic Relaxation

7Li stimulated-echo NMR and classical relaxation NMR techniques are jointly used for the first time for a comprehensive investigation of Li diffusion in layer-structured Li0.7TiS2. One single 2D Li diffusion process was probed over a dynamic range of almost 10 orders of magnitude. So far, this is the largest dynamic range being measured by 7Li NMR spectroscopy directly, i.e., without the help of a specific theoretical model. The jump rates obey a strict Arrhenius law, determined by an activation energy of 0.41(1)  eV and a preexponential factor of 6.3(1)×1012  s−1, and range between 1×10−1  s−1 and 7.8×108  s−1 (148–510 K). Ultraslow Li jumps in the kHz to sub-Hz range were measured directly by recording 7Li spin-alignment correlation functions. The temperature and, in particular, the frequency dependence of the relaxation rates fully agree with results expected for 2D diffusion. © 2006 The American Physical Society